[PATCH v3] drm/i915/dp: Add a meaningful return to intel_dp_read_dsc_dpcd

[Suraj Kandpal <suraj.kandpal@intel.com>]

Add a meaningful return to intel_dp_read_dsc_dpcd. This is to avoid
unwanted DPCD reads which are not needed once we know DSC DPCD
read fails. To do this convert drm_dp_dpcd_read to drm_dp_dpcd_read_data
which returns a meaningful error which can be propogated up when all
bits are not read.
While we are at it convert the drm_err in intel_dp_read_dsc_dpcd to
drm_dbg_kms. This is because we do not want a hard ERROR when we
call this function, during the intel_dp_detect phase since AUX may not
be up, it is expected to fail but we do not expect a failure in read
when we call intel_dp_dsc_get_sink_cap so we move the drm_err there.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
---
V1 -> V2:
-Commit message fixup (Jani)
-Convert drm_dp_dpcd_read to drm_dp_dpcd_read_data (Jani)
-Propogate the error sent by drm_dp_dpcd_read_data up (Jani)
-Use %pe and ERR_PTR() to log the extact error (Jani)

V2 -> V3:
-No need for the extra drm_err (Ankit)

 drivers/gpu/drm/i915/display/intel_dp.c | 31 +++++++++++++++----------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 79fd3b8d8b25..380d9801c377 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4281,20 +4281,24 @@ static bool intel_dp_get_colorimetry_status(struct intel_dp *intel_dp)
 	return dprx & DP_VSC_SDP_EXT_FOR_COLORIMETRY_SUPPORTED;
 }
 
-static void intel_dp_read_dsc_dpcd(struct drm_dp_aux *aux,
-				   u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
-{
-	if (drm_dp_dpcd_read(aux, DP_DSC_SUPPORT, dsc_dpcd,
-			     DP_DSC_RECEIVER_CAP_SIZE) < 0) {
-		drm_err(aux->drm_dev,
-			"Failed to read DPCD register 0x%x\n",
-			DP_DSC_SUPPORT);
-		return;
+static int intel_dp_read_dsc_dpcd(struct drm_dp_aux *aux,
+				  u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
+{
+	int ret;
+
+	ret = drm_dp_dpcd_read_data(aux, DP_DSC_SUPPORT, dsc_dpcd,
+				    DP_DSC_RECEIVER_CAP_SIZE);
+	if (ret) {
+		drm_dbg_kms(aux->drm_dev,
+			    "Could not read DSC DPCD register 0x%x Error: %pe\n",
+			    DP_DSC_SUPPORT, ERR_PTR(ret));
+		return ret;
 	}
 
 	drm_dbg_kms(aux->drm_dev, "DSC DPCD: %*ph\n",
 		    DP_DSC_RECEIVER_CAP_SIZE,
 		    dsc_dpcd);
+	return 0;
 }
 
 static void init_dsc_overall_throughput_limits(struct intel_connector *connector, bool is_branch)
@@ -4345,8 +4349,9 @@ void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
 	if (dpcd_rev < DP_DPCD_REV_14)
 		return;
 
-	intel_dp_read_dsc_dpcd(connector->dp.dsc_decompression_aux,
-			       connector->dp.dsc_dpcd);
+	if (intel_dp_read_dsc_dpcd(connector->dp.dsc_decompression_aux,
+				   connector->dp.dsc_dpcd) < 0)
+		return;
 
 	if (drm_dp_dpcd_readb(connector->dp.dsc_decompression_aux, DP_FEC_CAPABILITY,
 			      &connector->dp.fec_capability) < 0) {
@@ -4376,7 +4381,9 @@ static void intel_edp_get_dsc_sink_cap(u8 edp_dpcd_rev, struct intel_connector *
 	if (edp_dpcd_rev < DP_EDP_14)
 		return;
 
-	intel_dp_read_dsc_dpcd(connector->dp.dsc_decompression_aux, connector->dp.dsc_dpcd);
+	if (intel_dp_read_dsc_dpcd(connector->dp.dsc_decompression_aux,
+				   connector->dp.dsc_dpcd) < 0)
+		return;
 
 	if (connector->dp.dsc_dpcd[0] & DP_DSC_DECOMPRESSION_IS_SUPPORTED)
 		init_dsc_overall_throughput_limits(connector, false);
-- 
2.34.1